Project description:Cartilage aging is a quintessential feature of knee osteoarthritis, and extracellular matrix (ECM) stiffening is a typical feature of cartilage aging. However, the mechanism of ECM stiffening to influence chondrocytes and downstream molecules is still poorly understood. Here, we mimicked the physiological and pathological stiffness of human cartilage by using polydimethylsiloxane-based substrates. We show that the epigenetic regulation of Parkin by histone deacetylase 3 (HDAC3) represents a new mechanosensitive mechanism by which the stiff matrix affects the physiology of chondrocytes. We found that ECM stiffening could accelerate the senescence of cultured chondrocytes in vitro, and also found that stiff ECM downregulated HDAC3, drove Parkin acetylation to activate excessive mitophagy, and accelerated chondrocyte senescence and osteoarthritis in mice. In contrast, intra-articular injection of adeno-associated virus expressing HDAC3 restored the young phenotype of aged chondrocytes stimulated by ECM stiffening and alleviated osteoarthritis in mice. Our findings indicate that changes in the mechanical properties of ECM initiate pathogenic mechanotransduction signals, promote the acetylation of Parkin and hyperactivate mitophagy, and damage the health of chondrocytes. These findings may provide new insights into how the mechanical properties of ECM regulate chondrocytes.
Project description:As the unique cell type in articular cartilage, chondrocyte senescence is a crucial cellular event contributing to osteoarthritis development. Here we show that clathrin-mediated endocytosis and activation of Notch signaling promotes chondrocyte senescence and osteoarthritis development, which is negatively regulated by myosin light chain 3. Myosin light chain 3 (MYL3) protein levels decline sharply in senescent chondrocytes of cartilages from model mice and osteoarthritis (OA) patients. Conditional deletion of Myl3 in chondrocytes significantly promoted, whereas intra-articular injection of adeno-associated virus overexpressing MYL3 delayed, OA progression in male mice. MYL3 deficiency led to enhanced clathrin-mediated endocytosis by promoting the interaction between myosin VI and clathrin, further inducing the internalization of Notch and resulting in activation of Notch signaling in chondrocytes. Pharmacologic blockade of clathrin-mediated endocytosis-Notch signaling prevented MYL3 loss-induced chondrocyte senescence and alleviated OA progression in mice. Our results establish a previously unknown mechanism essential for cellular senescence and provide a potential therapeutic direction for OA.
Project description:Osteoarthritis (OA) is a widespread age-related joint disease caused by the gradual loss of chondrocyte function along with age. Here, we found that UFMylation modification was lower-leveled in senescent cartilage, mediated chondrocyte senescence and OA phenotypes through targeting CAVIN1, which acted as a stimulator in chondrocyte senescence, mainly through promoting CPT1 expression and activating fatty acid β-oxidation (FAO). Physiologically, FAO was at a very low level in chondrocytes, while the anomalous activation of FAO accelerated chondrocyte senescence. UFMylation of CAVIN1 promoted its binding with TRIP12, leading to ubiquitination degradation. Therefore, UFMylation played a pivotal role in post-translationally modification of CAVIN1. Polymeric micellar nanoparticles (NPs) conjugated with UFM1 improved the stability of UFM1 recombinant protein (UFM1-rp), and extended the retention time of UFM1-rp in the mouse joint cavity. The administration of UFM1 into mouse joints using an advanced NP delivery system is effective in attenuating age-related pathogenesis. Therefore, we uncovered a previously unknown mechanism, UFM1-CAVIN1-CPT1 axis, in the protection of OA progression and constructed a new drug for OA treatment, and have provided important preliminary evidence toward the translation of our findings into clinical usage.
Project description:Pericentric heterochromatin silencing at mammalian centromeres is essential for mitotic fidelity and genomic stability. Defective pericentric silencing is observed in senescent cells, aging tissues, and mammalian tumors, but the underlying mechanisms and functional consequences of these defects are unclear. Here, we uncover a pivotal role of the human SIRT6 enzyme in pericentric transcriptional silencing, and this function protects against mitotic defects, genomic instability, and cellular senescence. At pericentric heterochromatin, SIRT6 promotes deacetylation of a new substrate, histone H3 lysine K18 (H3K18), and inactivation of SIRT6 in cells leads to H3K18 hyperacetylation and aberrant accumulation of pericentric transcripts. Strikingly, RNAi-depletion of these transcripts rescues the mitotic and senescence phenotypes of SIRT6-deficient cells. Together, our findings reveal a new function for SIRT6 and H3K18Ac regulation at heterochromatin, and demonstrate the pathogenic role of de-regulated pericentric transcription in aging- and cancer- related cellular dysfunction. H3K18ac, H3K9ac, H3K9me3, H3K56ac and Input ChIP-seq for U2OS cell
Project description:Receptor-interacting protein kinase 1 (RIP1)-mediated necroptosis plays a vital role in various diseases, but the involvement of RIP1 and its functional mechanism in osteoarthritis pathogenesis remains largely unknown. To identify molecular targets of RIP1 in chondrocytes, RNA sequencing was performed in chondrocytes treated with adenovirus expressing RIP1 or vector control. We found that 9857 genes were differentially expressed in chondrocytes after RIP1 overexpression. GO analysis indicated that DNA replication, chromosome segregation and regulation of cell cycle process were upregulated, while terms including cartilage development, skeletal system development, extracellular matrix organization, skeletal system morphogenesis, chondrocyte differentiation, collagen fibril organization and limb development were downregulated. Pathway analysis revealed that IL-17 signaling pathway, cell cycle, DNA replication, proteasome, TNF signaling pathway, cellular senescence and p53 signaling pathway were significantly upregulated by RIP1, meanwhile, ECM-receptor interaction, other glycan degradation and glycosaminoglycan degradation were downregulated. These results underscore the importance of RIP1 in OA by perturbing a series of essential events during disease progression such like cell cycle regulation, chondrocyte differentiation, inflammation and ECM remodeling.
Project description:Chromobox homolog 4 (CBX4), a component of polycomb repressive complexes 1 (PRC1), plays important roles in the maintenance of cell identity and organism development through epigenetic silencing. However, it remains unclear whether CBX4 regulates the homeostasis of human stem cells. Here, we demonstrate that CBX4 counteracts human mesenchymal stem cell (hMSC) aging via the maintenance of nucleolar homeostasis. CBX4 protein decreases in aged hMSCs, and targeted knockout of CBX4 in young hMSCs destabilizes nucleolar heterochromatin, increases ribosome biogenesis, and accelerates cellular senescence. CBX4 maintains nucleolar homeostasis by recruiting fibrillarin at nucleolar rDNA repeats, limiting excessive expression of rRNAs. Importantly, overexpression of CBX4 expression alleviates physiological hMSC aging as well as attenuates the development of post-traumatic osteoarthritis in mice. Taken together, our study uncovers a novel role of CBX4 in counteracting senescence by maintaining nucleolar homeostasis, providing a potential therapeutic target for aging-associated disorders.